Gain variable circuit and automatic gain control amplifier using the same

Abstract

A gain variable circuit includes a first load between a first supply voltage and a first output terminal outputting a first output signal; a second load between the first supply voltage and a second output terminal outputting a second output signal with phase reversed from the first output signal; a first differential circuit between the first and second output terminals and a first node that changes gains of the first and second output signals based on first and second complementary gain variable signals; a second differential circuit between the first and second output terminals and a second node that changes gains of the first and second output signals based on the first and second gain variable signals; and an amplification circuit between the first and second nodes and a second supply voltage node that amplifies the first and second output signals based on first and second complementary input signals.

1. A gain variable circuit comprising:
 a first load connected between a first supply voltage node, and a first output terminal that outputs a first output signal; 
 a second load connected between the first supply voltage node, and a second output terminal that outputs a second output signal having phase reversed from a phase of the first output signal; 
 a first differential circuit that is connected between the first and second output terminals and a first node, and that changes gains of the first and second output signals responsive to a difference between first and second complementary gain variable signals; 
 a second differential circuit that is connected between the first and second output terminals and a second node, and that changes the gains of the first and second output signals responsive to a difference between the first and second gain variable signals; and 
 an amplification circuit that is connected between the first and second nodes and a second supply voltage node, and that amplifies the first and second output signals responsive to a difference between first and second complementary input signals, 
 wherein the first differential circuit comprises
 a first transistor that is connected between the first output terminal and the first node, and that has a state of conduction controlled by the first gain variable signal, and 
 a second transistor that is connected between the second output terminal and the first node, and that has a state of conduction controlled by the second gain variable signal, and 
 
 the second differential circuit comprises
 a third transistor that is connected between the first output terminal and the second node, and that has a state of conduction controlled by the second gain variable signal, and 
 a fourth transistor that is connected between the second output terminal and the second node, and that has a state of conduction controlled by the first gain variable signal. 
 
 
     
     
       2. The gain variable circuit of  claim 1 , wherein the amplification circuit comprises:
 a fifth transistor that is connected between the first node and the second supply voltage node, and that has a state of conduction controlled by the first input signal; and 
 a sixth transistor that is connected between the second node and the second supply voltage node, and that has a state of conduction controlled by the second input signal. 
 
     
     
       3. The gain variable circuit of  claim 2 , wherein the first and second loads have a same resistance value; the first, second, third, and fourth transistors have the same transistor characteristics; and the fifth and sixth transistors have the same transistor characteristics. 
     
     
       4. The gain variable circuit of  claim 1 , wherein the first and second loads are resistors. 
     
     
       5. The gain variable circuit of  claim 1 , wherein the first and second loads are transistors. 
     
     
       6. An automatic gain control amplifier comprising:
 the gain variable circuit of  claim 1 ; 
 a one-tier or multiple-tiered differential amplification circuit that differentially amplifies the first and second output signals of the gain variable circuit and outputs complementary third and fourth output signals; and 
 a feedback circuit that feeds back and inputs an amount of variation of the third and fourth output signals to the gain variable circuit as the first and second gain variable signals.